Kinematics of line-plane subassemblies in Stewart platforms

Trabajo presentado al ICRA 2009 celebrado en Kobe (Japón) del 12 al 17 de mayo.When the attachments of five legs in a Stewart platform are collinear on one side and coplanar on the other, the platform is said to contain a line-plane subassembly. This paper is devoted to the kinematics analysis of this subassembly paying particular attention to the problem of moving the aforementioned attachments without altering the singularity locus of the platform. It is shown how this is always possible provided that some cross-ratios between lines - defined by points in the plane- are kept equal to other cross-ratios between points in the line. This result leads to two simple motion rules upon which complex changes in the location of the attachments can be performed. These rules have interesting practical consequences as they permit a designer to optimize aspects of a parallel robot containing the analyzed subassembly, such as its manipulability in a given region, without altering its singularity locus.This work was supported by the project 'Analysis and motion planning of complex robotic systems' (4802). This work has been partially supported by the Spanish Ministry of Education and Science, under the I+D project DPI2007-60858.Peer Reviewe

Analysing the singularities of 6-SPS parallel robots using virtual legs

A virtual leg in a 6-SPS parallel robot is defined as a leg whose length is determined by the lengths of a subset of the actual legs of the robot. This necessarily implies that this subset of legs defines a rigid subassembly. In this paper, we consider four different rigid subassemblies, and show how the singularities of a robot containing one or several of these subassemblies are modified when substituting its actual legs by virtual legs.Peer Reviewe

Singularity-invariant leg substitutions in pentapods

6 páginas, 5 figuras, 4 tablas.-- Trabajo presentado a la IROS 2010 celebrada en Taipei (Taiwan) del 18 al 22 de Octubre.A pentapod is usually defined as a 5-degree-of-freedom fully-parallel manipulator with an axial spindle as moving platform. This kind of manipulators have revealed as an interesting alternative to serial robots handling axisymmetric tools. Their particular geometry permits that, in one tool axis, inclination angles of up to 90 degrees are possible thus overcoming the orientation limits of the classical Stewart platform.This work has been partially supported by the Spanish Ministry of Education and Innovation, under the I+D project DPI2007-60858.Peer reviewe

Self-motions of pentapods with linear platform

We give a full classification of all pentapods with linear platform possessing a self-motion beside the trivial rotation about the platform. Recent research necessitates a contemporary and accurate re-examination of old results on this topic given by Darboux, Mannheim, Duporcq and Bricard, which also takes the coincidence of platform anchor points into account. For our study we use bond theory with respect to a novel kinematic mapping for pentapods with linear platform, beside the method of singular-invariant leg-rearrangements. Based on our results we design pentapods with linear platform, which have a simplified direct kinematics concerning their number of (real) solutions.Comment: 28 pages, 5 figure

Singularity Analysis of PAMINSA Manipulators

International audiencePAMINSA (PArallel Manipulator of the I.N.S.A.) is a new family of parallel manipulators from four to six degrees of freedom (DOF), which have been developed at the I.N.S.A. in Rennes. The particularity of these manipulators is the decoupling of displacements in the horizontal plane from its translation along the vertical axis. Such a decoupling improves some mechanical properties of the manipulator making it more efficient. In this paper a singularity analysis of PAMINSA with four, five and six degrees of freedom is presented. The nature of each kind of singularity is discussed

Using the FRDPARRC design methodology to drive innovation in the HETDEX PFIP support adjustable strut assembly

textThis thesis provides background information on the Hobby-Eberly Telescope (HET), HET Dark Energy Experiment (HETDEX), Gough-Stewart platforms (GSP), the Prime Focus Instrument Package (PFIP) support structure, and the design methodology used to design said support structure. Each component is analyzed from the point of view of Professor Alex Slocum’s FRDPARRC design methodology. Each aspect of the design is shown to have been derived by following the steps of Slocum’s design method. Material selection, manufacturing techniques, and integration of off-the-shelf components into the support system are also discussed in reference to FRDPARRC. The assembly procedure for the PFIP structure is outlined. Finally, using specific examples from the detailed design, the FRDPARRC method itself is analyzed and its ability to drive innovation in design is evaluated.Mechanical Engineerin

Design and analysis of kinematically redundant planar parallel manipulator for isotropic stiffness condition

Parallel manipulators are a form of closed loop linkages and have a wide range of applications e.g. surgical robots, flight simulators, pointing devices etc. Parallel mechanisms have many advantages over serial manipulator. Higher accuracy, stiffness and increased payload capacity are the characteristics of parallel manipulator. In spite of many advantages, they have limited workspace and more singularity regions. So, redundant architectures have become popular. However, redundancy leads to infinite solutions for inverse kinematic problem. The current work addresses this issue of resolving the redundancy of kinematically redundant planar parallel manipulators using optimization based approach. First the conventional non-redundant 3-RPR planar parallel manipulator is presented. Afterwards the kinematically redundant counterpart 3-PRPR is discussed and actuation redundant 4-RPR has been touched upon briefly. Computer simulations have been performed for the kinematic issues using MATLAB programme . The workspace of redundant and non-redundant parallel manipulators have been obtained. The generalized stiffness matrix has been derived based upon the Jacobian model and the principle of duality between kinematics and statics. A stiffness index has been formulated and the isotropy of stiffness index is used as the criterion for resolving redundancy. A novel spiral optimization metaheuristics has been used to achieve the isotropic stiffness within the selected workshape and the results are compared against particle swarm optimization. The results obtained from the novel Spiral optimization are found to be more effective and closer to the objective function as compared to the particle swarm optimization. Optimum redundant parameters are obtained as a result of the analysis. A wooden skeletal prototype has also been fabricated to enhance the understanding of the mechanism workability

Design of Novel Sensors and Instruments for Minimally Invasive Lung Tumour Localization via Palpation

Minimally Invasive Thoracoscopic Surgery (MITS) has become the treatment of choice for lung cancer. However, MITS prevents the surgeons from using manual palpation, thereby often making it challenging to reliably locate the tumours for resection. This thesis presents the design, analysis and validation of novel tactile sensors, a novel miniature force sensor, a robotic instrument, and a wireless hand-held instrument to address this limitation. The low-cost, disposable tactile sensors have been shown to easily detect a 5 mm tumour located 10 mm deep in soft tissue. The force sensor can measure six degrees of freedom forces and torques with temperature compensation using a single optical fiber. The robotic instrument is compatible with the da Vinci surgical robot and allows the use of tactile sensing, force sensing and ultrasound to localize the tumours. The wireless hand-held instrument allows the use of tactile sensing in procedures where a robot is not available

Reliability assessment approach through geospatial mapping for offshore wind energy

To meet the increased energy demands, uphold commitments made in the Paris agreement and provide energy security to its consumers, the United Kingdom is rapidly expanding its wind energy industry at offshore locations. While harnessing the improved wind resource further offshore, the industry has faced reliability challenges in the dynamic marine environment which contribute to an increase in the cost of energy. This thesis promotes the argument for location - intelligent decisions in the industry by developing a methodology to allocate a combined risk - return performance metric for offshore locations. In the absence of comprehensive spatially distributed field reliability data for offshore wind turbines, the limit state design methodology is employed to model structural damage. Exposed to stochastic loading from wind and wave regimes, offshore wind turbines are fatigue-critical structures. The aero- and hydro-dynamic loads at representative sites across eight sub-regions in the UK continental shelf are quantified by processing modelled metocean data through established aero-hydro-servo-elastic design tools. These simulated loads and the inherent material fatigue properties provide site-specific lifetime accumulated damage. Normalising this damage based on the potential energy production at each site provides an improved understanding of the feasibility of the sub-region for offshore wind deployment. Results indicate that although sheltered sub-regions display lower resource potential, they have the benefit of the reduced associated structural damage compared to more dynamic locations. A similar observation is made when the methodology is employed on a larger scale incorporating the UK continental shelf and its adjoining areas. Furthermore, not only the energy potential displays an increase with an increase in distance-to-shore, but also the damage per unit energy produced. The research outcomes of this project are useful for identifying the potential of structural reserves for lifetime extension considerations as more turbines reach their design lifetimes. Additionally, it may be used to inform design parameters, optimise siting of future installations and determine suitable maintenance strategies to improve the economic viability of offshore wind

The 24th Aerospace Mechanisms Symposium

The proceedings of the symposium are reported. Technological areas covered include actuators, aerospace mechanism applications for ground support equipment, lubricants, latches, connectors, and other mechanisms for large space structures